Zinc ammonium chloride fluxes



Patented Aug. 23, 1938 ZINC AMMONiUM CHLORIDE FLUXES Raymond J. Kepfer, Lakewood, Ohio, .assignor,

by meme mours 8: poration of Delaware assignments, to E. 1. du Pont de Ne- Company, Wilmington, DeL, a cor- No Drawing. Application March 5, 1936, Serial No. 67,306

1 Claim.

This invention relates to zinc ammonium chloride galvanizing fluxes, and is particularly directed to processes wherein unsatisfactory zinc ammonium chloride galvanizing fluxes are made suitable for use with foaming agents by reducing the amount of sulfates present as impurities.

In hot dip galvanizing, a bath of molten zinc is covered with a flux. As articles to be galvanized are lowered into the molten zinc bath they, of course, first pass thru the flux where they are cleaned and prepared for the reception of a metal coating.

It has heretofore been the practice to employ foaming agents such as giycerine, tallow, and soap bark with the flux in order to produce a foam or froth. Ordinarily the foaming agent and flux are separately added, as required, to the zinc bath. Sometimes the zinc ammonium chloride flux and foaming agent in predetermined proportions are simultaneously. added to a zinc bath either by adding a mixture of flux and foaming agentdirectly to the bath or by adding such a mixture to a pre-wash from which the metal being treated carries the flux and foaming agent to the bath.

The foam produced by means of foaming. agents serves to entrap vapors and gases and to retard the rate of volatilization of the flux. For galvanizing operations of this type it is essential that the foam be satisfactory in character and of sufficient thickness.

Galvanizers have frequently been confronted with the diificuity that, for no apparent reason, it is sometimes extremely difficult or even impossible to obtain a satisfactory foam. Sometimes by using a great excess of foaming agent it was possible to obtain a moderately satisfactory foam. In most instances, the diiliculties were surmounted only by purchasing a new lot of zinc ammonium chloride flux which would not be so unsatisfactory.

I have found that this hitherto unaccountable behavior on the part of zinc ammonium chloride fluxes is attributable to the presence therein of an excess of sulfate. When sulfates are present in excess of about 2% SO: in zinc ammonium chloride fluxes, it is difilcult or impossible to produce a satisfactory foam by the use of the customary foaming agents even when such agents are used in very large amounts. Without a satisfactory foam on the galvanizing bath, it is, of course, impossible to proceed with the galvanizing operations. It is also observed that when excessive amounts of sulfates are present in zinc ammonium chloride fluxes, there is excessive "fuming. That is, the ammonium chloride in the flux herein to the sulfate content in terms of the percentage of SO: found, in accordance with standard practice.

To render usable zinc ammonium chloride fluxes which contain excessive amounts of sulfates, it is only necessary to remove the sulfates in any desired manner. I have found it most satisfactory to remove so much of the sulfate as is necessary by adding an acid soluble barium salt, such as barium chloride or barium carbonate, to the flux while it is in dilute solution in the course of its manufacture. The resulting barium sulfate may be removed by decanting or filtering the solution.

Strangely enough, barium sulfate does not seem to exercise the deleterious effects experienced with most sulfates unless the barium sulfate is present in amounts exceeding about 5% as S03. If it is desired, therefore, to remove relatively small amounts of sulfate from concentrated zinc ammonium chloride liquors, the soluble barium salt may simply be added and the resulting barium sulfate included in the product. Of course, if this procedure is followed, great care must be exercised lest too large an amount of barium sulfate be present.

if the flux and foaming agent are to be added to a galvanizing bath indirectly by using the flux and foaming agent in a pre-dip, the excess of sulfate may be removed by adding a soluble barium salt to the pre-dip. Here again, care must be exercised lest the barium sulfate content be too great.

Zinc ammonium chloride fluxes superior to those heretofore offered the trade may be prepared by removing substantially all of the sulfate content. If it is not expedient to remove all of the sulfate, zinc ammonium chloride fluxes of very high quality may be prepared by treating the zinc ammonium chloride fluxes so that no more than about 0.1% S03 is present. If it is found desirable to remove still less of the sulfate, satisfactory zinc ammonium chloride fluxes comparable to the best commercial fluxes heretofore oflered the trade may be prepared by removing sulfate so that no preferred, however, to leave as much as 0.2% 80: in the flux because with this highest permissible S03 content, it is ordinarily necessary to add a little more foaming agent than would be required with the fluxes having a lower S03 content.

The following examples are given more fully to explain the practice of my invention.

Example I thereof. Using the sulfate-free zinc ammonium chloride flux, a foam blanket about four and a half inches thick was obtained. This foam lasted for about twenty four minutes, and there was very little fuming.

Example II Another commercial zinc ammonium chloride flux found unacceptable to the trade was analyzed and was found to contain 0.36% of sulfate computed as S03. Testing this flux on a galvanizing pot, a foam about one inch thick and which lasted for only about two minutes was obtained. Considerable fuming of the flux was observed, tho it was not quite as bad as the original flux mentioned in Example I. Following the procedure of this invention, the sulfates were removed from the flux by the use of barium chloride. The flux then led to the production of a foam which lasted for about twenty two minutes and which was about four and a half inches thick.

Example III A zinc ammonium chloride flux which was found unacceptable to the trade was analyzed and was found to contain 0.41% of sulfates computed as S03. This unsatisfactory flux produced a foam which lasted for about four minutes and was about one inch thick. This flux contained 0.7% of glycerine as a foaming agent. To reduce the content of sulfates in the flux, there was added thereto a sulfate-free zinc ammonium chloride flux which contained 0.7% of glycerine. The sulfate-free flux was added in an amount sufficient to bring the sulfate content of the mixture down to 0.05% computed as S03. The resulting mixture was used as a flux on a galvaniz ing pot and a foam which lasted for thirteen minutes and which was about four inches thick more than about 0.2% remains. It is not was obtained. Very little fuming was noted with.

the improved flux composition.

Example IV A commercial zinc ammonium chloride flux which contained 1.25% of soap bark as a foaming agent was analyzed and was treated to reduce the sulfate content to about 0.2% computed as S03. The flux was much improved, leading to the production of a foam which lasted for about six minutes, and which was about one and one-half inches thick. There was moderate fuming. This flux was made more acceptable by increasing the soap bark content to 2.5% after which there was obtained a foam three inches thick which lasted for fourteen minutes. The fuming was considerably lighter. It will be observed that at the upper limits of sulfate content specified by my invention, it is necessary to use a larger amount of foaming agents to produce entirely satisfactory results. The use of an excess of a foaming agent is, of course, expensive and undesirable, and it is generally preferable, therefore, to reduce the sulfate content as much as possible.

Example V A concentrated zinc ammonium chloride liquor which contained sulfates equivalent to 0.5% B01 was treated with barium chloride. The zinc ammonium chloride was crystallized from the solution and removed therefrom together with the barium sulfate. The flux thus produced was used on a galvanizing pot and, after adding foaming agents in the customary amount, there was obtained a foam about two and a half inches thick which lasted for about fourteen minutes. There was very little fuming. It is thus noted that barium sulfate equivalent to 0.5% S0: does not exercise the deleterious effects observed with equally large amounts of other sulfates. If barium sulfate be present in larger amounts, however, it adversely affects the characteristics of the flux.

While I have shown a number of specific procedures in the foregoing, it will readily be apparent that the sulfate content of zinc ammonium chloride fluxes may be reduced in varying amounts and by various procedures without departing from the spirit of this invention.

I claim:

In a process for the treatment of a zinc ammonium chloride galvanizing flux which contains sulfates and hence is unsatisfactory by reason of the poor foam produced when it is used with foaming agents, the flux containing no more than about 0.5% S03, the steps comprising treating the flux with a soluble barium compound to convert the sulfate to barium sulfate so that when used with foaming agents the flux will produce foams of satisfactory thickness and character.

RAYMOND J. IQEPFER. 

